When a senior Israeli official told Reuters that Binyamin Netanyahu would be drawing a red line on Iran's nuclear program, he was not kidding.

Speaking at the United Nations general assembly in New York, the Israeli prime minister unfolded a chart with a cartoon-style drawing of a nuclear bomb, and proceeded to draw on it with a red magic-marker.

"This is a bomb," he says. "This is a fuse."

Binyamin Netanyahu uses a graphic as he addresses general assembly at UN headquarters in New York. Photograph: Lu

The only peaceful way to prevent an Iranian nuclear bomb is to place a "clear red line" on uranium enrichment, Netanyahu said.

"A red line must be drawn ... on Iran's efforts to enrich uranium," he said. "Basically any bomb consists of explosive material and a mechanism to ignite it. ... In the case of Iran's plans, the gunpowder is enriched uranium. The fuse is a nuclear detonator." Netanyahu sad it was far more difficult for Iran to enrich uranium than to build the fuse.

He explained where where the red line on enriching uranium should be drawn. He said Iran is well into "the second stage" of enrichment. By next summer, they will move on to the final stage, he said. From there it's only a few months, maybe a few weeks, before they get enough enriched uranium for a bomb, he says.

"If these are the facts, where should a red line be drawn?" he asks.

Netanyahu took out a red marker. "Where should a red line be drawn? he says. "A red line should be drawn right here." He drew a line at the end of the "second stage," at 90% of the necessary enriched uranium for the first bomb.

It was an eye-catching, if bizarre, moment. And inevitably it drew polarised reactions.

Typically: this, from former White House press secretary Ari Fleischer:

Ari Fleischer (@AriFleischer)

Bibi's use of that chart was one of the most effective, gripping, uses of a chart I've ever seen. Is the world listening??

Speaking to press onboard his campaign plane, the Republican presidential nominee, Mitt Romney, says that he would press for an indictment of Iranian president Mahmoud Ahmadinejad on charges of inciting genocide